EVALUATION OF COMPLEMENT ACTIVITY BY AN ENZYME-IMMUNOASSAY

An ELISA-type assay useful for the evaluation of the complement activi ty in serum is described. Aggregated pooled human IgG (IgGn) prepared so as to exclude large and small aggregates, to resemble soluble circu lating immune complexes, was used to coat polystyrene microwells to se rve as initiator of complement activation. Fresh serum, at different d ilutions, as the source of the complement to be evaluated was added an d the plate incubated 90 min at 37-degrees-C. Then, a peroxidase-label ed antihuman C3c antibody was added to react with the bound C fragment s. This was followed by 2,2'-azino-di-3-ethyl benzothiazoline sulfonic acid (ABTS), as the color reagent used for detection of the enzyme ac tivity. In this system, theoretically, the levels of activating and re gulatory complement components are evaluated up to the level of C3 spl itting. The assay was applied in healthy volunteers to set normal valu es and in 15 patients suffering from systemic lupus erythematosus maki ng possible the differentiation of those with normal and low complemen t levels.